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Short Note on Sewage: Types, Pollutants, Collection, Treatment and Disposal
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A large portion of sewage when left untreated makes its way to the main water bodies. This produces a flock of diseases like diarrhea (responsible for many casualties among children), environmental degradation, and agricultural contamination. Unfortunately, the less privileged ones are mainly exposed to dirty canals and drain where they battle for their lives. A wide variety of bacteria, parasites, fungi, and viruses is present within sewage.
Countries are in a long battle against containing such problems. They are developing expensive treatment plants, pumping stations, and underground pipes. Some organizations are involved in developing less expensive sewage systems that are effective.
You might also be interested in reading more Wastewater.
Overview Of Sewage
Sewage forms by a community of people as a result of the accumulation of various types of BW remains of water from a storm, industrial effluents, and so on. Handling or recycling sewage requires significant investment and manpower.
During the early days when such systems were scarce, sewers were left discharged into the main river body streams such as lake, ocean, or bay. Nowadays, a separate plant is built to cater to these problems known as a wastewater treatment plant. The strategies laid to handle such problems include separating surface runoff from sewage and handling the separation of greywater from toilet water. Communities are making proper sewage management a norm in industrialized localities.
Types Of Sewage
The nature and type of sewage can be broadly classified into three groups. These are:
- Domestic Or Sanitary Sewage
These types of wastes are mainly carried off by people residing in residential areas and institutions in the form of feces and urine, laundry wastes, food wastes, and so on.
- Commercial Wastes
These types of wastes are categorized as domestic if their nature of flow is of household ones. Commercial wastes are mainly released from shops and service establishments with a focal point of serving communities. Wastes that originate from industrial processes are known as industrial wastewater which forms by either manufacturing or production of goods.
- Surface Runoff
Precipitation flowing on a surface to a defined channel is known as surface runoff. They carry all the chemicals from the atmosphere while dissolving and leaching materials from soil and vegetation. After collecting all these pollutants, they flow to a certain connection point.
Know more about Quality and Characteristics of Sewage here.
Pollutants Of Sewage
Untreated sewage consists of mainly harmful substances like pathogens (bacteria and virus), nutrients (phosphorus and nitrogen) organic matter (solids). It also includes toxic chemicals like PAHs, PCBs, dioxins, furans, phenols, pesticides, and chlorinated organics.
Below Is a detailed analysis of such pollutants.
- Organic Pollutants And Nutrients
As seen above, sewage has complex chemical characteristics consisting of chemical mixtures. They include highly concentrated ammonium, nitrate, phosphorus, nitrogen, high alkalinity, high conductivity, pH ranging between 7 and 8.
To determine and measure the parameters of sewage, Biochemical oxygen demand and chemical oxygen demand are used. These tests point out the load organic carbon carries into the environment.
- Pathogens
Pathogen simply means any organism that can produce diseases. As sewage consists largely of human feces, pathogens are commonly found in them with any of the four types.
- Bacteria
Different types of bacteria are present like salmonella, campylobacter, shigella, vibrio cholerae. The majorities of bacteria that have μM between 0.15 and 700 in length are mostly harmless and are beneficial to humans. Whereas a small group of pathogenic bacteria may prove dangerous and lead to infectious diseases. These types of bacteria are potent enough to enter the cell and cause damage to the immune system of the body by producing endotoxins. Pneumonia is one such globally common disease caused by pathogens.
- Viruses
Potential viruses like hepatitis A, enteroviruses, rotavirus. Viruses are typically small particles ranging between 20 to 300 nanometers in length that contain DNA or RNA. Viruses undergo a replication process that requires them to host a cell. Chickenpox, influenza, mumps, measles, Ebola, HIV, are such diseases caused by viral pathogens.
- Protozoa
Such as Entamoeba, histolytica, cryptosporidium parvum are a group of individual-celled eukaryotes which feed on organic matter like microorganisms, debris, or organic tissues. They are known to possess behaviours like animals by their methods of predation and motility.
Read more about the Quality of Water, here.
- Parasites
Roundworm, hookworm, and whipworm are some parasites present in sewage water. They are visible to the naked eye. These worms’ dwell and breed in their living host receiving nourishment and refuge while mutilating the nutrients of the host. They are also known to manipulate their host’s immune system by a secreting method called immunomodulatory products. This allows them to live and grow for many years.
Traditional techniques are undertaken to monitor sewage that produces disease and benign organisms. These techniques are manual-based like staining, filtering, and examining collected samples under a microscope. However, DNA sequencing can provide effective testing and results by looking for rare organisms, discovering new species, attempting eradication, and so on. This sequencing method is also known as metagenomics.
- Micro-pollutants
Sewage contains a large concentration of pharmaceuticals (roughly 70%) that comes from households alone, 20 percent coming from livestock farming, hospital effluent (5%), and the rest coming from runoffs. Trihalomethanes are also present due to past disinfection.
Sewage also contains nutrients that could cause eutrophication, a process by which a body of water gets enriched by a variety of minerals and nutrients. This may lead to ecotoxicity.
Read more about Water Supply, here.
Health And Environmental Aspects Of Sewage
Health Aspects
As per GESAMP (2001), coastal marine environment contamination by sewage gives rise to several infectious diseases. These are linked to swimming and bathing in marine waters and by consuming seafood. When humans are exposed to various toxins which are associated with algae, significant risk factors also arise.
Pathogens are responsible for most of the illnesses which are infectious or biological agents causing widespread diseases. Diarrhea, typhoid, cholera, and hepatitis A are acute diseases caused by them. These types of bacteria are known to survive in the sea for several weeks. They have the potency to survive in water and infect marine life and eventually dwell in them for a long time. Hepatitis, on the other hand, can remain active in the sea for over a year. Sewage also contains industrial or chemical wastes like nutrients, industrial chemicals, pharmaceuticals, and heavy metals, thereby causing an additional threat to human health.
Environmental Aspects
Organisms require chemical nutrients to reproduce and survive. Excessive nutrients are released in the marine environment through fertilizers from agriculture, and nitrogen oxides that form by burning fossil fuels. In cities, sewage is the main source of nutrients, and agriculture is the leading source in rural areas. Increased nutrients induce the growth of a wide variety of plants and decay, a process known as eutrophication. Algae plants increase in population causing a lack of oxygen and sunlight in water. This creates a fuss in marine life as water becomes inhabitable for them. Some algae are toxic enough to kill dolphins, whales, and other species causing a huge loss to mankind.
Check out this article on Design of Sewer here.
Collection Of Sewage
Sewage is collected by sewer pipes and is transferred for treatment or is discharged. This process is called a sewage system. Lack of sewerage systems is taken care of by collecting waste from households through pipes into septic tanks and is then treated or is collected for disposal.
There are many ways of collecting sewage. Some of them are discussed below.
- Combined Systems
A mixture of both domestic and storm sewage is known as combined sewers. They usually contain vast parameters of pipes as they must deal with a variety of waste. They are not developed in big cities as wastewater plants cannot handle stormwater.
- Separate Systems
They are meant to carry either domestic sewage or stormwater, but not both. Storm sewers handle the surface runoff to a point of a river or in a stream where it is disposed of. Storm sewers are developed with a section of enclosed concrete pipes.
- Alternative Systems
When the cost of building gravity sewers crosses significant expenses due to the low concentration of population, three alternatives are derived to combat this. These are small-diameter sewers, pressure sewers, and vacuum sewers. In the small-diameter, floating solids are removed by using septic tanks. Pressure sewers are utilized in flat areas or where rocky excavations are needed. Vacuum sewers flow by gravity directly into a tank from where vacuum pumps pull it.
Know more about Solid Waste Management here.
Treatment Of Sewage
Sewage is treated to remove the toxins and contaminants to produce solid and liquid that is preferably suitable for discharge or reuse. This process of treatment is known as sewage treatment, also a kind of waste management. Sewage sludges are formed during the treatment and further sludge treatment is required for disposal. Several approaches are undertaken to stabilize biomass and reduce solid content. The most popular anaerobic digestion is chosen due to its cost-effective nature and bioenergy production. Sewage sludges are best used by agriculture and to produce electricity by converting biogas.
Some of the common sewer treatments include: –
- On-site Disposal Systems
Wastes Recurring from toilets, laundry, bathroom, and sink makes their way towards a pipe to a septic tank. Effluent is disposed of through its disposal and is soaked in the surrounding soil.
- The Effluent Wastewater Disposal System
Community effluents are carried off by pipes to the lagoon. These pipes are built mainly to serve houses in the community.
- Full Sewage System
All the waste from houses, showers, toilets, are carried by pipes and then pumped to a lagoon. Full sewage systems are of three types. One goes untreated, the other passes through a process of cutting blades, and the final gets treated in a septic tank.
Learn more about Water Treatment, here.
Disposal Of Sewage
Sewage disposal has several ways. Two are considered vital. Sewage is disposed of using on-site sanitation procedures or removed by waterborne sewer systems.
Domestic waste is collected by pipes called sanitary sewers which go to a discharge point. Collecting stormwater is taken care of by storm sewers. It is then discharged and drained in an area.
Municipalities have their own system called sewage treatment plants where it directly feeds all into the system. Sewage lagoons directly flow into a lagoon of still water.
Know more about Disposal of Sewage here.
Reuse Of Treated And Untreated Sewage
Sewage can also be used to convert biogas by a process known as anaerobic digestion. Farmers use untreated wastewater for irrigation purposes. Cities help provide fresh produce considered attractive for farmers. Since there is no alternative for farmers, they use polluted water to fill the gap of the scarcity of water. However, there can be many health-related issues if they continue doing this. Pathogens may be present in the raw vegetables and consuming them can lead to a variety of diseases. International water management helps farmers reduce the risk of using wastewater by stopping irrigation before harvesting. This allows the pathogens to die in the sunlight.
Learn more about Water Pollution, here.
Now that you have developed an understanding of key aspects of sewage, it is time to enhance your knowledge further. Download the Testbook App now and access the best online learning resources curated by experts.
Sewage FAQs
What is sewage? How is it treated?
Sewage is the result of water emerging from the use by human beings. For example, flushing toilets, bathing water, industrial wastes, and so on. It is treated by treatment plants where it is discharged into a public sewer.
What are the constituents of sewage?
Domestic sewage contains 300 to 450 mg/liter of biodegradable oxygen and chemical oxygen demand. It contains harmful bacteria that can prove dangerous for human beings.
How to reuse treated sewage?
Biogas is formed by sewage known as anaerobic digestion. This can be used as fuel for heating purposes in the village community. Biogas can also be used for gas stations.
What are the steps of sewage treatment?
On-site disposal systems where wastes make their way to a septic tank through a pipe. Effluent wastes are carried off to a lagoon. Full sewage systems may comprise treated and untreated sewage.
How is sewage collected?
Sewage is collected by pipes and then goes for treating purposes or is discharged. Combined systems and separate systems are used in the process of collecting sewage. Combined carries both domestic and stormwater whereas separate systems deal with either domestic or stormwater but not both.